The major objective of this proposal is to evaluate the role of ventricular receptors in the control of vascular tone in physiologic and pathologic states. 1) Since it is not known if ventricular baroreceptors respond to physiologic pressures, an analysis of the determinants, threshold and gain of left ventricular baroreceptor activity will be performed with square wave and sine wave pressure variations produced in a left ventricular balloon with a servocontrolled pressure pump in dogs on cardiopulmonary bypass. 2) Because activation of arterial baroreceptors alters responses to chemoreceptor stimulation, we plan to evaluate interactions between reflexes arising in ventricular receptors and in carotid receptors. 3) We also plan to determine if right ventricular stretch produces reflex vasodilation in dogs on cardiopulmonary bypass in which changes in pulmonary arterial and atrial pressures are minimized. 4) Finally, the role of ventricular receptors in the autonomic responses to ventricular fibrillation will be studied, and the effects of myocardial ischemia on the autonomic responses to ventricular defibrillation will be evaluated.